1. Field of the Invention
The present invention relates to a load-lock device which stands by with a plurality of semiconductor wafers loaded thereon to cooperate with a transport device for in order transporting the semiconductor wafers to a processing chamber and, more particularly, to a load-lock device having a structure to transport semiconductor wafers to a processing chamber efficiently.
2. Description of the Related Art
A conventional semiconductor processing apparatus has employed a load-lock device which stands by with a plurality of semiconductor wafers loaded thereon in order to transport objects to be processed such as semiconductor wafers to a processing chamber in order for processing therein. FIG. 1A shows a conventional single chamber type load-lock device. The load-lock device comprises a chamber 1 whose interior is evacuated, wafer holding means 6 for loading a plurality of semiconductor wafers 4 thereon, and a transport mechanism 7 for in order transporting the semiconductor wafers 4 from the wafer holding means 6 to a processing chamber 2. The chamber 1 includes a gate valve 3 for establishing communication between the processing chamber 2 and the chamber 1 and a front door 5 through which the wafer holding means 6 loaded with the semiconductor wafers 4 is transported in and out.
After the front door 5 is opened to allow a wafer holding means 6 loaded with the semiconductor wafers 4 to be transported into the chamber 1, the front door 5 is closed to evacuate the interior of the chamber 1. Then, the gate valve 3 is opened, and the transport mechanism 7 transports one of the semiconductor wafers 4 into the processing chamber 2. The semiconductor wafer 4 is returned to its initial position in the wafer holding means 6 after being processed in the processing chamber 2, and the next semiconductor wafer 4 is then transported into the processing chamber 2. When all of the semiconductor wafers 4 in the wafer holding means 6 are thus processed, the gate valve 3 is closed and the front door 5 is opened to remove the wafer holding means 6 from the chamber 1. Thereafter, another wafer holding means 6 is transported into the chamber 1 through the front door 5.
However, such a conventional single chamber type load-lock device has had the problem of low productivity because the processing apparatus must be stopped during the time required for replacing wafer holding means.
Under such circumstances, load-lock devices having a plurality of chambers have been developed to improve productivity. FIG. 1B schematically shows a conventional load-lock device having a plurality of chambers. This device comprises one transport mechanism 10, two load-lock chambers 8, 9 connected to the transport mechanism 10 through gate valves 12 and two processing chambers 13, 14 connected to the transport mechanism 10 through gate valves 12. The chambers 8, 9 respectively includes wafer holding means 16, 17 for standing by with a predetermined number of semiconductor wafers loaded thereon and door valves 11A, 11B for transporting processed semiconductors in order out of the chamber.
The door valves 11A, 11B of the respective load-lock chambers 8, 9 are opened to load a predetermined number of semiconductor wafers 18 into the wafer holding means 16, 17 and, thereafter, the interior of the chambers 8, 9 are evacuated. Then, a first gate valve 12A is opened to transport the semiconductor wafer 18 from the first load-lock chamber 8 to the processing chambers 13, 14 in order. When the process is completed, the semiconductor wafers 18 in the processing chambers 13, 14 are returned to the first load-lock chamber 8, and the first gate valve 12A is closed. Thereafter, a second gate valve 12B is opened to transport the semiconductor wafers 18 from the second load-lock chamber 9 to the processing chambers 13, 14 in order. Meanwhile, the door valve 11A of the first load-lock chamber 8 is opened to remove the processed semiconductor wafers in order and to load the next semiconductor wafers in the wafer holding means 16.
Such a conventional load-lock device having a plurality of chambers has reduced the so-called idle time of the processing chambers to thereby improve productivity.
However, such a conventional load-lock device having a plurality of chambers has problems as described below.
In a conventional load-lock device having a plurality of chambers, in order to improve the rate of operation of the processing chambers, while semiconductor wafers in the first load-lock chamber are processed, processed semiconductors must be removed from the second load-lock chamber to load new semiconductor wafers therein and the door valve must be closed to evacuate the second load-lock chamber to put in a stand-by state. If this operation can not be carried out while the semiconductor wafers are being processed, new semiconductor wafers can not be transported into the processing chambers in spite of which the process has already been completed, which leaves the processing chambers in a vacant state. Such a risk is significant especially for processes such as thin film processing which are performed in a short processing time. The same situation is likely to occur when a great number of chambers are used.
The number of load-lock chambers may be increased in order to avoid this. The conventional structure in which a plurality of load-lock chambers are disposed horizontally increases the size of an device as a whole, which goes against the needs in the market for reduction of the space for such an device. Conventional load-lock devices have such limitations from the view point of hardware.
It is therefore an object of the invention to provide a load-lock device and a method in which the space for an device can be reduced and productivity can be improved.
It is another object of the invention to provide a load-lock device and a therefor in which high productivity can be maintained even for many processing chambers and processes performed in a short processing time.